The present invention relates to means for the protection of personnel, equipment and the environment in the event of a blow-out during the drilling of a submerged well. It relates more particularly, but not exclusively to drilling carried out from a floating support on a very deep stretch of water, where intervention by means of underwater equipment is out of the question. It is necessary, under these circumstances, to provide a safety installation which can be activated rapidly and reliably from the floating drilling support in the event of failure of the conventional protective means, such as the units for shutting off the well or their control means.